A driving method for a low-noise switched reluctance motor and a cooking machine adopting the method

Abstract

A driving method for a low-noise switched reluctance motor, characterized by comprising the following steps: Step 1, start; Step 2, calculate T; Step 3, within T, perform carrier randomization on the PWM wave, and the carrier at the turn-off angle θ off is always at zero potential; Step 4, use the random PWM wave to excite the current phase winding; Step 5, determine whether an interruption has arrived. If so, commutate according to the conduction sequence in the current rotation direction, and return to Step 2; if not, continue to execute Step 4. The present invention also discloses a cooking machine that operates with a switched reluctance motor adopting the above driving method. Compared with the prior art, the advantages of the present invention are as follows: Without changing the fixed duty cycle (i.e., the total conduction time) within the original carrier working time, the duty cycle is redistributed, and the carrier frequency is randomized, so that the end of the last carrier is always at zero potential, avoiding the sudden change of voltage from +U to -U, thereby reducing the electromagnetic noise and the vibration noise.

Description

Technical Field

[0001] The present invention relates to a switched reluctance motor, in particular to a driving method for a low-noise switched reluctance motor and a cooking machine adopting the driving method of the switched reluctance motor. Background Art

[0002] With the continuous improvement of people's requirements for diet and health preservation, various food cooking machines have entered people's daily lives. The working principle of a food cooking machine is that the blades at the bottom of the mixing cup rotate at a high speed, and under the action of water flow, the food is repeatedly broken. In addition to the function of breaking food, high-end food cooking machines also have the functions of stir-frying and baking.

[0003] The control parameters of a switched reluctance motor are numerous, including phase voltage U, phase current i, turn-on angle θ on and turn-off angle θ off etc. The motor control methods of a switched reluctance motor usually include three methods: current chopping control (CCC), voltage chopping control (CVC), and angle position control (APC). Among them, the voltage chopping control method is a relatively commonly used method in the motor control strategy. This control method is to adopt a PWM working mode for the power switch device IGBT while keeping the turn-on angle θ on and turn-off angle θ off unchanged, that is, by adjusting the duty cycle of the PWM wave, the average voltage across the phase winding is adjusted, and then the magnitude of the phase winding current is indirectly changed, so as to realize the control of the motor. As Figure 1 shown, the phase current waveform of the switched reluctance motor when the duty cycle of the PWM wave is changed in the electric state is given.

[0004] At present, when adopting the voltage chopping control method, the carrier frequency of its PWM is usually fixed. As Figure 2 shown, within the actual working time of the PWM wave, the number of PWM waves is not necessarily an integer, and the duty cycle of the PWM wave will change according to the change of the load. This leads to the situation that when the load is large, at the turn-off angle θ off moment, there is easily a negative step change of the voltage from +U to -U, resulting in a greater free vibration due to the current mutation. That is to say, near the integer multiple of the switching frequency, there will be obvious electromagnetic noise and vibration.

[0005] To solve the above noise problem, in the prior art, a driving device for a switched reluctance motor disclosed in a Chinese invention patent with the patent number ZL 97117996.4, titled "Driving Device for Switched Reluctance Motor", includes three delayers. These delayers are used to delay the A-phase, B-phase, and C-phase rotor position signals output by the A-phase, B-phase, and C-phase position sensors by a predetermined time respectively, and then output them as the gate signals of the lower-arm switching devices of the switched reluctance motor driving circuit, so that the turn-off of the lower-arm switching devices is delayed by a predetermined time compared to the turn-off of the upper-arm switching devices, thereby canceling the radial force generated during turn-off and reducing the noise of the switched reluctance motor.

[0006] However, in the above patent, an external hardware "delayer" is required to achieve turn-off delay and thus reduce noise. This not only increases the manufacturing cost of the device but also makes the overall structure of the device more complex. Additionally, when using this hardware device "delayer" for control, errors in the final control accuracy may occur due to possible deviations in the design and manufacturing of the hardware itself. In actual use, it is still impossible to accurately and reliably achieve effective control of the motor noise.

[0007] In summary, for the noise problem existing in the process of controlling a switched reluctance motor by using a voltage chopping control method in the prior art, there is currently no practical and reliable solution, and further improvement and perfection are awaited. Summary of the Invention

[0008] The first technical problem to be solved by the present invention is to provide a driving method for a low-noise switched reluctance motor with a simple implementation method and higher control reliability in view of the above-mentioned prior art situation.

[0009] The second technical problem to be solved by the present invention is to provide a cooking machine adopting the above-mentioned driving method for a switched reluctance motor in view of the above-mentioned prior art situation.

[0010] The technical solution adopted by the present invention to solve the above first technical problem is: a driving method for a low-noise switched reluctance motor, characterized in that the driving method includes the following steps:

[0011] Step 1: The program starts and the motor starts.

[0012] Step 2: The current phase winding is conducted, and the actual working time T of the PWM wave in the current phase winding is calculated.

[0013] Step 3: Within the actual working time T, the PWM wave is subjected to carrier randomization processing to obtain a random PWM wave in which the carrier is always at zero potential at the turn-off angle θ off moment.

[0014] Step 4: Excite the current phase winding with the random PWM wave obtained in Step 3;

[0015] Step 5: Determine whether an external interrupt has arrived. If so, the current motor commutes according to the conduction sequence in the rotation direction and returns to Step 2; if not, continue to execute Step 4.

[0016] Preferably, the actual working time of the PWM wave in the current phase winding where n is the real-time speed of the motor, θ on is the turn-on angle of the current winding, θ off is the turn-off angle of the current winding.

[0017] Preferably, the carrier randomization process in Step 3 includes the following major steps:

[0018] Step A: Random selection of the actual number of carriers N set ;

[0019] Step B: According to the actual number of carriers N set , perform random allocation of the time of each carrier period of the PWM wave;

[0020] Step C: For each carrier period time, random allocation of the +U voltage excitation time T on (i) and the zero voltage excitation time T off (i) of the PWM wave;

[0021] Step D: The motor obtains a random PWM wave with the number of carriers being N set , the +U voltage excitation time of each carrier being T on (i) and the zero voltage excitation time of each carrier being T off (i).

[0022] More preferably, the random selection of the actual number of carriers N in Step A specifically includes the following steps: set ;

[0023] Step 3-1: According to the preset value range [f min , f max of the PWM carrier frequency, obtain the range of the allowable number of carriers N within the actual working time T as: Tf min ≤N≤Tf max , where f min is the preset minimum value of the PWM carrier frequency, and f max is the preset maximum value of the PWM carrier frequency;

[0024] Step 3-2: Among [Tf min , Tf maxRandomly select N within the range set as the actual number of carrier waves, where N set is a positive integer.

[0025] As a further preference, the randomized allocation of the time of each carrier period of the PWM wave in step B specifically includes the following steps:

[0026] Step 3-3: According to the randomly selected actual number of carrier waves N set , obtain the minimum carrier time of the PWM wave as N set / f max , where f max is the preset maximum value of the PWM carrier frequency;

[0027] Step 3-4: Calculate the remaining time T l = T - N set / f max of the PWM wave in the current phase winding, and equally divide the remaining time T l into N set parts with equal probability, and the value of each part is x i T l , where x i is a random variable, 0 < x i < 1 and x i is randomly selected;

[0028] Step 3-5: Obtain the time of each carrier period of the PWM wave as T f (i) = 1 / f max + x i T l , where 0 ≤ i < N set , and i is an integer.

[0029] As a further preference, the randomized allocation of the +U voltage excitation time T on (i) and the zero voltage excitation time T off (i) of the PWM wave in step C specifically includes the following steps:

[0030] Step 3-6: Set the effective duty cycle of the PWM wave as D, and set the +U voltage excitation time of the PWM wave in each carrier period as T on (i), and equally distribute the total +U voltage excitation time D×T of the current phase winding into each carrier period, and satisfy the following conditions: where T on (i) < T f (i), T f (i) is the time of each carrier period of the PWM wave, T on (i) is randomly selected, 0 ≤ i < N set, where i is an integer;

[0031] Step 3-7: Calculate the zero-voltage excitation time of the PWM wave in each carrier period as T off (i) = T f (i) - T on (i), where 0 ≤ i < N set , where i is an integer.

[0032] Preferably, the minimum value f min of the preset PWM carrier frequency in Step 3-1 ranges as follows: f min ∈ [3×10 3 , 5×10 3 Hz.

[0033] Preferably, the maximum value f max of the preset PWM carrier frequency in Step 3-1 ranges as follows: f max ∈ [1.5×10 4 , 1.7×10 4 Hz.

[0034] Preferably, the value range [f min , f max of the preset PWM carrier frequency in Step 3-1 is [4×10 3 , 1.6×10 4 Hz. The higher the carrier frequency, the greater the switching loss; the lower the carrier frequency, the larger the current ripple. To ensure the normal and stable operation of the motor while reducing the switching loss, it is optimal to take the carrier frequency within the range of [4×10 3 , 1.6×10 4 Hz.

[0035] Considering the stability and reliability of the actual operation of the motor, to reduce the current ripple and noise at the same time, preferably, the actual number of carriers N set is optimally taken as the largest positive integer among the allowable number of carriers N.

[0036] The technical solution adopted by the present invention to solve the above second technical problem is: A cooking machine includes a switched reluctance motor, characterized in that: the switched reluctance motor operates using the driving method described above.

[0037] Compared with the prior art, the advantages of the present invention are as follows:

[0038] ①. Randomize the carriers so that the end of the last carrier is always at zero potential, avoiding the negative step of the voltage from +U to -U, thereby reducing electromagnetic noise and vibration noise.

[0039] ②. Based on the characteristics of the turn-on angle and turn-off angle of the switched reluctance motor, while ensuring that the fixed duty cycle (i.e., the total conduction time) within the original carrier working time remains unchanged, the duty cycle is redistributed to achieve random allocation of the carrier frequency. Since the carrier frequency is randomized, the carrier frequency after each commutation changes randomly. Compared with the traditional carrier with a fixed frequency, the sound heard by the human ear is no longer single, and the noise can be further reduced.

[0040] ③. Ensure the application of the secondary turn-off technology, so that the voltage of a certain phase winding changes from +U to 0 and then to -U during turn-off, which can effectively reduce the vibration during commutation, thereby further reducing the noise. Description of the Drawings

[0041] Figure 1 is the phase current waveform diagram of the switched reluctance motor under voltage PWM control in the prior art;

[0042] Figure 2 is the carrier voltage step waveform diagram of the switched reluctance motor under voltage PWM control in the prior art;

[0043] Figure 3 is the carrier voltage step waveform diagram of the switched reluctance motor of the embodiment of the present invention under voltage PWM control;

[0044] Figure 4 is the schematic diagram of the effective duty cycle of the PWM wave within the actual working cycle time of the embodiment of the present invention;

[0045] Figure 5 is the schematic diagram of the random carrier cycle time allocation of the PWM of the embodiment of the present invention;

[0046] Figure 6 is the control flowchart of the driving method of the low-noise switched reluctance motor of the embodiment of the present invention.

[0047] Figure 7 is the specific control method of the carrier randomization processing in the driving method of the low-noise switched reluctance motor of the embodiment of the present invention. Detailed Embodiment

[0048] The present invention will be further described in detail below in conjunction with the embodiments of the drawings.

[0049] The motor involved in this embodiment is a four-phase 8 / 6-pole switched reluctance motor. As Figure 3 shown, it is the main circuit diagram of the power converter with an asymmetric half-bridge topology adopted by the switched reluctance motor of this embodiment. Each phase has two main switch devices and a freewheeling diode. Each phase winding of the switched reluctance motor controls the energization and de-energization of the switch tube in the power converter by sending signals from the main control chip to achieve operation.

[0050] The voltage PWM control method is a relatively common method in the control strategy of switched reluctance motors. The basic principle of PWM speed control is to turn on and off the power supply at a fixed frequency and change the on-off time ratio (duty cycle) within a cycle according to needs to change the "duty cycle" of the voltage on the armature of the DC motor, thereby changing the average voltage and controlling the speed of the motor. However, during the actual working time of the PWM wave, when using a carrier with a traditional fixed frequency, at the turn-off angle θ off moment, there is an easy negative step change of the voltage from +U to -U, resulting in a sudden change in current and generating greater free vibration. That is to say, near the integer multiple of the switching frequency, obvious electromagnetic noise and vibration will exist.

[0051] For this reason, this embodiment proposes a driving method for a switched reluctance motor that can effectively reduce noise, and a food processor that operates using the driving method of the switched reluctance motor.

[0052] As Figure 6 shown, this embodiment discloses a driving method for a low-noise switched reluctance motor. The driving method includes the following steps:

[0053] Step 1: The program starts, the motor starts, and runs normally.

[0054] Step 2: When the current phase winding is conducting, calculate the actual working time T of the PWM wave in the current phase winding; among them, the actual working time of the PWM wave in the current phase winding where n is the real-time speed of the motor, θ on is the conduction angle of the current winding, and θ off is the turn-off angle of the current winding; in this embodiment, when the current phase winding is conducting, if the speed of the motor is 10,000 rpm, the conduction angle θ on =-3°, and the turn-off angle θ off =15°, then the actual working time T of the PWM wave is 300 us.

[0055] Step 3: During the actual working time T, perform carrier randomization processing on the PWM wave to obtain a random PWM wave whose carrier is always at zero potential at the turn-off angle θ off moment.

[0056] Step 4: Excite the current phase winding with the random PWM wave obtained in Step 3.

[0057] Step 5: Determine whether an external interruption has arrived (this interruption mainly refers to commutation). If so, the current motor commutes according to the conduction sequence in the rotation direction and returns to Step 2 to perform carrier randomization processing again; if not, continue to execute Step 4.

[0058] As Figure 7As shown, in the third step of this embodiment, the carrier randomization process is specifically implemented in the following manner:

[0059] Step A: First, the random selection of the actual number of carriers N set Specifically, it includes:

[0060] Step 3-1: According to the preset value range [f min , f max of the PWM carrier frequency, obtain the range of the allowable number of carriers N within the actual working time T as: Tf min ≤N≤Tf max ;

[0061] Step 3-2: Randomly select N min , Tf max within the range [Tf min , Tf max obtained in Step 3-1 as the actual number of carriers, where N set is a positive integer. set Take positive integers.

[0062] Among them, f min is the preset minimum value of the PWM carrier frequency, and the preset minimum value f min of the PWM carrier frequency has a value range of: f min ∈[3×10 3 , 5×10 3 Hz, f max is the preset maximum value of the PWM carrier frequency, and the preset maximum value f max of the PWM carrier frequency has a value range of: f max ∈[1.5×10 4 , 1.7×10 4 Hz; The higher the carrier frequency, the greater the switching loss of the driver, and even the situation where the motor will howl and not rotate. While the lower the carrier frequency, the motor will run smoothly, the current ripple is large, resulting in large vibration and noise. In order to ensure the normal and stable operation of the motor and extend the service life of the switch, in this embodiment, the preset value range [f min , f max of the PWM carrier frequency is preferably taken as [4×10 3 , 1.6×10 4 Hz.

[0063] According to the actual working time T = 300us calculated in the previous step two, the allowable number of carriers is 1.2≤N≤4.8, and the actual number of carriers N set can take values 2, 3, or 4. When N set is small, the switching loss is small, but the current ripple is large. When N setWhen taking the maximum value, although the switching loss is large, the current ripple is small and the noise is correspondingly reduced. Considering actual applications, in order to reduce the ripple and simultaneously reduce the noise to improve the stability and reliability of the motor operation, the actual number of carrier waves N set Taking the largest positive integer 4 among the allowable number of carrier waves N as the best.

[0064] Step B: Secondly, according to the actual number of carrier waves N set , perform random allocation of the time of each carrier period of the PWM wave, specifically including:

[0065] Step 3-3: According to the actual number of carrier waves N selected in Step Four set , the minimum carrier time of the PWM wave is obtained as N set / f max ;

[0066] Step 3-4: Calculate the remaining time T of the PWM wave in the current phase winding l =T - N set / f max , and equally divide the remaining time T l into N set parts, and the value of each part is x i T l , where x i is a random variable, 0 < x i < 1, and x i is randomly selected and can take any number of integers or decimals;

[0067] Step 3-5: Obtain the time of each carrier period of the PWM wave as T f (i) = 1 / f max +x i T l , where 0 ≤ i < N set , and i takes an integer. As Figure 5 shown is the schematic diagram of the random carrier period time allocation obtained by dividing the actual working time of the PWM wave into N set carriers.

[0068] Step C: Then, for each carrier period time, implement random allocation of the +U voltage excitation time T on (i) and the zero voltage excitation time T off (i) of the PWM wave; specifically including:

[0069] Step 3-6: Set the effective duty cycle of the PWM wave as D, and set the +U voltage excitation time of the PWM wave in each carrier period as T on (i), and equally distribute the total +U voltage excitation time DT of the current phase winding to each carrier period, and satisfy the following conditions: Among them, T on (i) < T f (i), T on (i) is randomly selected, 0 ≤ i < N set , i is an integer; for example, within the actual working time T of the PWM wave, there are a total of 4 PWM carriers, Figure 4 as shown is the schematic diagram of the effective duty cycle of the current PWM wave;

[0070] Step 3 - 7, calculate the zero - voltage excitation time of the PWM wave within each carrier period as T off (i) = T f (i) - T on (i), where 0 ≤ i < N set , i is an integer;

[0071] Step 3 - 8, the motor is excited for the current phase winding according to the random PWM wave with the number of carriers being N set , the +U voltage excitation time of each carrier being T on (i) and the zero - voltage excitation time of each carrier being T off (i).

[0072] Step D, finally, the motor obtains a random PWM wave with the number of carriers being N set , the +U voltage excitation time of each carrier being T on (i) and the zero - voltage excitation time of each carrier being T off (i).

[0073] This embodiment is aimed at when the motor starts and operates in the normal working state. If the motor has a starting fault or a fault occurs during operation, this program is exited and fault handling is performed. For the motor fault judgment and handling, various methods in the prior art can be used to achieve, which do not belong to the protection scope of the present invention and will not be elaborated here.

[0074] The driving method of this embodiment adopts the voltage chopping control method. While ensuring that the fixed duty cycle (total conduction time) within the original carrier working time T remains unchanged, the duty cycle and the time of each carrier period are randomly distributed, and an integer number of carrier numbers within the T working time is intercepted. At the same time, it is ensured that the +U voltage excitation time T on (i) of the PWM wave within each carrier period is less than the total time T f (i) of each carrier period, that is, the PWM carrier is loaded in the way of +U → 0 → +U → 0... and the last ending carrier is always at zero potential. At the instant when the winding is turned off, it is avoided that the winding voltage steps negatively from +U to -U, thereby reducing vibration and vibration noise.

[0075] Because when exciting each phase winding, the on and off times of the duty cycle within the PWM carrier working time are random, and the PWM carrier frequency is not fixed. This varying frequency can also reduce noise and avoid the concentrated noise generated by a fixed frequency. The driving method of this embodiment does not require changing the hardware structure of the original motor and can be implemented through software, with a simpler implementation method, better practicability and reliability.

[0076] This embodiment also discloses a cooking machine, which includes a switched reluctance motor, and the switched reluctance motor operates by using the driving method of the low-noise switched reluctance motor described in this embodiment.

Claims

1. A driving method for a low-noise switched reluctance motor, characterized in that The described driving method includes the following steps: Step 1: The program starts and the motor is started. Step 2: The current phase winding is turned on, and the actual working time T of the PWM wave in the current phase winding is calculated. Step 3: During the actual working time T, perform carrier randomization on the PWM wave to obtain a random PWM wave in which the carrier is always at zero potential at the turn-off angle θ off moment; Step 4: The current phase winding is excited with the random PWM wave obtained in Step 3. Step 5: Determine whether an interruption has arrived. If so, the current motor commutes according to the conduction sequence in the rotation direction and returns to Step 2; if not, continue to execute Step 4.

2. The driving method of the low-noise switched reluctance motor according to claim 1, characterized in that: The actual working time of the PWM wave in the current phase winding in Step 2 where n is the real-time speed of the motor, and θ on is the conduction angle of the current winding, and θ off is the turn-off angle of the current winding.

3. The driving method of the low-noise switched reluctance motor according to claim 1, characterized in that: The carrier randomization process in the described Step 3 includes the following steps: Step A, randomly select the actual number of carriers N set ; Step B: According to the actual number of carriers N set , perform randomized allocation of the time of each carrier period of the PWM wave; Step C: For each carrier cycle time, the +U voltage excitation time T of the PWM wave on (i) and the zero voltage excitation time T off (i) for randomized allocation; Step D: The motor obtains a carrier number of N set and the +U voltage excitation time of each carrier is T on (i) and the zero voltage excitation time of each carrier is T off (i) random PWM wave 4. The driving method of the low-noise switched reluctance motor according to claim 3, characterized in that: The actual number of carriers N in the step A set The random selection specifically includes the following steps: Step 3-1. According to the value range of the preset PWM carrier frequency [f min , f max , obtain the range of the allowable number of carriers N within the actual working time T as: Tf min ≤N≤Tf max , where f min is the minimum value of the preset PWM carrier frequency, and f max is the maximum value of the preset PWM carrier frequency; Step 3-2. Randomly select N within the range of [Tf min , Tf max as the actual number of carriers, where N set is a positive integer. set ​ 5. The driving method of the low-noise switched reluctance motor according to claim 3, wherein: The random allocation of each carrier cycle time of the PWM wave in the described Step B specifically includes the following steps: Step 3-3: According to the randomly selected actual number of carriers N set , the minimum carrier time of the PWM wave is obtained as N set / f max , where f max is the preset maximum value of the PWM carrier frequency; Step 3-4, calculate the remaining time T of the PWM wave in the current phase winding l = T - N set / f max , and equally divide the remaining time T l into N set equal parts, and the value of each part is x i T l , where x i is a random variable, 0 < x i < 1 and x i is randomly selected; Step 3-5: Obtain that the time of each carrier period of the PWM wave is T f i = 1 / f max +x i T l , where 0 ≤ i < N set , and i is an integer 6. The driving method of the low-noise switched reluctance motor according to claim 3, wherein: The +U voltage excitation time T of the PWM wave in step C on (i) and the zero voltage excitation time T off (i) The randomized assignment specifically includes the following steps: Step 3-6: Set the effective duty cycle of the PWM wave as D, and set the +U voltage excitation time of the PWM wave within each carrier period as T on (i), evenly distribute the total +U voltage excitation time D×T of the current phase winding into each carrier period, and satisfy the following conditions: where, T on (i) < T f (i), T f (i) is the time of each carrier period of the PWM wave, T on (i) is randomly selected, 0 ≤ i < N set , and i is an integer; Step 3-7: Calculate the zero-voltage excitation time of the PWM wave within each carrier period as T off T(i) = T f T(i) - T on T(i), where 0 ≤ i < N set , and i is an integer.

7. The driving method of the low-noise switched reluctance motor according to claim 4, characterized in that: The minimum value f of the preset PWM carrier frequency in the said step 3-1 min has a value range of: f min ∈ [3×10 3 , 5×10 3 Hz.

8. The driving method of the low-noise switched reluctance motor according to claim 4, characterized in that The maximum value f of the preset PWM carrier frequency in the said step 3-1 max has a value range of: f max ∈[1.5×10 4 , 1.7×10 4 Hz.

9. The driving method of the low-noise switched reluctance motor according to claim 4, characterized in that: The value range of the preset PWM carrier frequency [f min , f max in the step 3-1 is [4×10 3 , 1.6×10 4 Hz.

10. The driving method of the low-noise switched reluctance motor according to claim 4, characterized in that: The actual number of carriers N in step 3-2 set takes the value of the largest positive integer among the allowed number of carriers N.

11. A cooking machine, comprising a switched reluctance motor, characterized in that: The described switched reluctance motor operates using the driving method described in any one of claims 1 to 10.

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